The work in these laboratories has for some years focused on mammalian meiosis, with particular emphasis on oogenesis. We have been concerned with the cytologic, biochemical, ultrastructural and hormonal aspects of this process in mammals, particularly human. This attention stems from the fundamental interest in the causes of abnormal progeny in the human, particularly the progeny who result from numerical or structural abnormalities in the germ cell genome. The present application takes a new direction built upon the body of data and hypotheses which hane resulted from this interest. The application process to examine (1) the characteristics of fetal mouse oogonia proceeding toward meiosis (2) chemical and conformational modifications of nuclei and mitochondria of oogeneis and spermatogenesis and (3) the model that distortion of pairing of homologues by microtubule inhibiting agents affects recombination. These studies bring together the biology of germ cell development and the simultaneous changes in the nucleus.